1. Field of the Invention
The present invention relates to a method for writing servo information on a magnetic recording disk.
2. Description of the Background Art
Digital magnetic recording devices for data storage generally comprise a thin film magnetic recording disk and a head or transducer which is moved along or above the surface of the rotating disk to electromagnetically read and write information on the disk. Advanced thin film magnetic recording disks comprise a rigid substrate, a magnetic layer such as a cobalt- based metal alloy, a protective amorphous carbon layer, and a lubricant layer such as a perfluoropolyether disposed on the carbon overcoat.
During operation of the disk drive system, an actuator mechanism rotated by a voice coil motor (vcm) moves the magnetic transducer to a desired radial position on the surface of the disk rotating on a spindle where the head electromagnetically reads or writes data. Usually, the head is integrally mounted in a carrier or support referred to as a "slider". A slider generally serves to mechanically support the head and any electrical connections between the head and the rest of the disk drive system. The slider is aerodynamically shaped to glide over moving air and maintain a uniform distance from the surface of the rotating disk, thereby preventing the head from undesirably contacting the disk.
The head reads or writes data to or from a large number of concentric circular tracks formed on the magnetic disk. The shape and position of each track is defined by magnetic servo information (track identification information) permanently written onto the disk for each track. Servo information ensures that during operation of the disk drive, the head is centered over the desired track. Individual servo information is imbedded around the circular track in either a sector or continuous fashion. In order to avoid reading and writing data errors, it is desired that each track be a perfect circle correctly centered on the disk. Deviation of a track from a perfect circle or off center will cause it to be squeezed together with adjacent tracks. During the writing process, data can be overwritten on a squeezed adjacent track, resulting in loss of data. Therefore, it is important that servo information which defines the track position and shape be accurately written on the disk.
The magnetic servo information is generally written on a magnetic recording disk using the recording device's own head while the disk is spinning on the spindle of the recording device. However, it is important during the process to accurately position and hold the actuator so that the head is at the desired radial location on the disk. After servo information has been written on a track, the actuator is then repositioned to write the next track. One method for accurate positioning of the actuator during the servo track write (STW) process involves using an external positioner to locate the actuator and hold it steady while the track is being written. This external device is often called a "pusher".
The pusher contacts the actuator of the disk drive, pushes it to the desired location, and then holds it steady while the track is being written. This sequence of "push" and "hold steady" is repeated until the entire surface of the disk has been written with concentric circular servo tracks. The pusher generally consists of a mechanical arm and pin that reaches inside the drive and physically contacts the actuator. A contact force may be maintained between the pusher pin and actuator by putting a DC current in the VCM which results in a DC force on the actuator to hold it against the pin. The pusher arm/pin is connected to a motor which positions the arm/pin. The position of the pusher is determined with a measurement device (i.e. encoder, or laser, etc.), and this position is controlled by a closed-loop feedback control system. The closed-loop control allows the pusher to move a desired distance and then lock itself into position while the track is being written.
The use of a STW pusher requires that there be physical access into the interior of the completed disk drive so that it can contact the actuator. Access may be accomplished by an opening or slot in either the cover or base casting to accommodate the full-stroke of the pusher as it moves the actuator over the disk surface.
In order to achieve accurate writing of servo information, JP6-124522, published May 6, 1994, discloses placement of a plate between adjacent disk during the writing process to decrease the vibration of the disks and decrease the quantity of air colliding against the STW head arm. It is desirable to minimize vibrations of the drive during STW in order to facilitate the writing of circular tracks. The presence of vibrations during STW can result in wavy (or non-circular) tracks. However, the arrangement disclosed in this patent application is cumbersome. JP1-92986, published Apr. 12, 1989, discloses evacuating air from the disk drive device during the servo write process. However, since the slider requires a gaseous medium to fly over the disk, evacuation can result in the head crashing into the disk surface. Therefore, there still is a need in the art for an improved process for writing servo information to a magnetic recording device.
It is an object of the present invention to provide an improved process for writing servo information to a magnetic recording device.
Other objects and advantages will be apparent from the following disclosure.